Background:
Presbycusis (age-related hearing impairment: ARHI) is believed to be a typical complex disorder associated with both genetic factors and environmental factors (“complex ARHI”). However, a small portion of patients with CDH23 mutations exhibit an ARHI-like phenotype (“monogenic ARHI”). It is an interesting question as to the difference between the two types of ARHI from the clinical viewpoint as well as audiogram configurations.

Material and Methods:
The detailed clinical courses of two cases of “monogenic ARHI” caused by CDH23 mutations were evaluated. In addition, statistical classification of audiogram configurations was used to determine whether or not “monogenic ARHI” can be differentiated from the other clusters with high frequency involved hearing loss.

Results:
Although onset age of the present two cases was somewhat earlier than commonly encountered in ARHI, clinical features were very similar to presbycusis, with slowly progressive high frequency involved hearing loss.

Conclusions:
The present data strongly supports the view that there are at least two types of ARHI and a particular type of ARHI (late onset hereditary hearing loss) is monogenically inherited. It may be possible to differentiate those subtypes through statistical classification of audiogram configurations.